1. Field of the Invention
The present invention relates to a device for detecting a pressure in a combustion chamber of an internal combustion engine.
2. Description of the Related Art
Currently, in an internal combustion engine such as an automobile engine, the driving conditions thereof are controlled electrically. For example, when suitably controlling an ignition timing to prevent knocking, it is necessary to detect a pressure in the combustion chamber, called "a combustion pressure" hereinafter, with a high accuracy.
Among the conventional devices for detecting the combustion pressure, Japanese Unexamined Utility Model Publication No. 58-146941 discloses a device in which an annular piezoelectric sensor is arranged inside of a cylinder head gasket, i.e., on a combustion chamber side thereof, and a change of distance between a cylinder head and the cylinder head gasket due to a combustion is detected by the piezoelectric sensor, to thereby calculate the combustion pressure.
In the above device, the cylinder head gasket equipped with the piezoelectric sensor is tightened between the cylinder head and the cylinder block by bolts passing therethrough, therefore, in such a construction, if the cylinder head is displaced by a combustion or explosion in the combustion chamber, the piezoelectric sensor will be bent to thereby generate an electric charge, and the combustion pressure can be obtained by detecting the electric charge. Nevertheless, since a tightening force of the bolts varies widely in practice, the output characteristics of the sensor are influenced by the variations of the tightening force, and thus the accuracy of the detection of the combustion pressure is lowered.